I have some friends whose daughter has fibromyalgia and have searched the net for this and chronic fatigue. The medical nutrition therapy for both of these is just a healthy balanced diet. Fibromyalgia is a form of arthritis and chronic fatigue is related to Epstein-Barr which involves the liver.
As for candida, there is lots of misinformation out there with people claiming to have candida in their gastrointestinal tract, blood or other body parts. They have been informed to cut out everything with yeast because they seem to think that eating yeast is the cause of the candida. This practice is not supported by research. In fact, in some parts of the human body, yeast is normally present and a benefit to health as in the colon (large bowel). Candida infections are common in the oral cavity of persons undergoing chemotherapy and are called thrush. It is effectively treated with an antibiotic.
Haven’t had anyone ask about leaky gut and am not familiar with such. From a practical side, if one’s gut (stomach or intestines) were “leaking” the abdominal cavity would have a terrible infection and the person would experience extreme pain that would probably need emergency surgery. If you find websites specific to candida or leaky gut that are supported by current nutrition research and practice, please email those URLs to me.